A British ISIS fighter has taken to Twitter to ask his fellow Muslim brothers to target UK civilians to avenge the death of a Saudi Arabian woman in Essex.

Nahid Almanea, 31, was killed as she walked along a Colchester footpath. Essex Police said the attack could have been provoked by the University of Essex student's attire. She was wearing a full-length robe, known as Abaya as well as a Hijab headscarf.

Following her death, fanatic Abu Rashash Britani, who has previously claimed that he and other insurgents will return to Britain after they finished fighting in Iraq and Syria, has now called for a revenge attack.

He tweeted: "These kuffar getting out of hand, dare they touch a #Muslimah. I call upon any brother to take up a knife and kill as they did #colchester."

He then compared her killing to Drummer Lee Rigby outside his barracks in Woolwich last year.

"#colchester attack is cowardly act. At least when our noble brothers, killers of #leerigby did so they killed a soldier not a civilian," he added.

Twitter has since suspended Britani's account.

His threats coincide with the announcement of Lahoor Talabani, director of counter terrorism for the Kurdistan Regional Government (KRG) that up to 450 Britons have joined the ranks of ISIS fanatics and could attack the UK. He told Sky News that the offensive in the north of the country by ISIS should not be viewed as an attack only on the Iraqi government.

"According to the intelligence we have, just Britain alone have around 400 to 450 known people fighting amongst the ranks of ISIS," he said.

Prime Minister David Cameron also warned that ISIS was plotting terror attacks on the UK and that militants returning from fighting in Iraq and neighbouring Syria were now a greater threat than those from Afghanistan.